[Qemu-devel] [virtio] virtqueue request size

[Vasile Catalin-B50542]

I'm trying to work out virtqueue from the virtio API.
I've been able to send a message from guest to qemu, but there is something
strange that I don't understand.
virtqueue_get_avail_bytes() returns 0 number of "in" bytes, but if I 
hard code
iov_to_buf() to get 5 bytes, it actually gets my message.
What am I missing out?
Here is the essential code so far:
Guest:
    probe function:
        vq = virtio_find_single_vq(vdev, recv_done, "input");
    triggered send function:
        sg_init_one(&sg, buf, size);
        if (virtqueue_add_inbuf(vq, &sg, 1, buf, GFP_KERNEL) < 0)
            BUG();
        virtqueue_kick(vq);

Qemu:
    realize function:
        vcrypto->vq = virtio_add_queue(vdev, 8, handle_input);
    handle_input:
        virtqueue_pop(vcrypto->vq, &elem);
        eprintf("request size is %u", get_request_size(vcrypto->vq, 
100)); // prints size 0
        iov_to_buf(elem.in_sg, elem.in_num, 0, buffer, 5); // hardcoded 
to 5 bytes for now
    get_request_size:
        virtqueue_get_avail_bytes(vq, &in, &out, quota, quota); // 
quota = 100
        return in;